The present invention relates to a target, as well as to the picture tube equipped with such a target and the complete apparatus formed by the tube and its reading means.
The target according to the invention can be constructed in different ways, e.g. a photoconductive target made from one of the conventional materials such as antimony sulphide (Sb.sub.2 S.sub.3), lead oxide (PbO), etc., a photodiode mosaic target formed in a silicon substrate, a pryoelectric target, etc. The invention is applicable in general terms to all types of targets used in picture tubes.
On one of its faces, the target has a conductive plate or signal plate on which is sampled the electrical signal corresponding to the different points on the target, during the point by point scanning of the other face thereof, by the reading electron beam. At each point, the beam deposits a certain quantity of electrons to compensate the effect produced at this point in the target by incident radiation. This quantity, read in the signal plate circuit, constitutes the signal of the point.
One of the problems encountered in connection with such targets is that of the noise inherent in such systems, which has numerous causes, including the actual target. Furthermore, one of the causes of this noise is the capacitance between the signal plate and the system earth or ground.